<bump>
What ratio?
Thread Starter
|
Senior User
Joined: Jul 2009
Posts: 295
Likes: 0
From: Rocky Mtns. of Colorado
What ratio?
I have a stock '98 E-350 passenger van with a 6.8L. The van is often loaded and pulling a 6000# trailer at 8000' in the Colorado mountains. This van is not used for long trips or interstate highway travel, so while good fuel economy is desirable, it is not the priority. It has a rear axle code of 34, which indicates a standard 3.73 rear end. I am going to change the gearing and would like input on what to change it to. I'm thinking 4.30, but would like to hear your opinions.
Thanks!
Thanks!
Super Moderator
Joined: Apr 2004
Posts: 34,475
Likes: 2,800
Tire size and transmission ratio for OD are needed. You can put them in here:
Novak Conversions - Gearing & Gearing Math for Jeeps
What does it rev now? What are the torque and hp peaks? What is mpg now? Why do you want shorter gears?
Novak Conversions - Gearing & Gearing Math for Jeeps
What does it rev now? What are the torque and hp peaks? What is mpg now? Why do you want shorter gears?
Thread Starter
|
Senior User
Joined: Jul 2009
Posts: 295
Likes: 0
From: Rocky Mtns. of Colorado
Thanks for the OD ratio Mark.
The van is used at high elevation, often loaded with 10 - 15 adults and pulling a 6000# trailer up some rather steep climbs. A 3.73 rear end ratio seems to me like a highway/fuel economy motivated gearing. We have another van with a 7.5L and 4.10 gears, and it seems to pull better despite the slightly lower HP and torque. Since we don't do much highway driving, it made sense to look at gearing the rear end with a bigger gear to accommodate the type of work it does.
I believe when ordered new, this van came with 3.73, but could be ordered with 4.10 for towing applications. So a 4.10 should be fine. But, I think that 4.10 was a "compromise" ratio that improved towing without sacrificing fuel economy too much. That's great for applications that spend a lot of time on the highway. But, since we don't need the top end much, and are not too worried about the MPG, and since the 4.10 "compromise" doesn't take into account our 8000' elevation, I started thinking that 4.30 or 4.56 might be a better choice.
The van is used at high elevation, often loaded with 10 - 15 adults and pulling a 6000# trailer up some rather steep climbs. A 3.73 rear end ratio seems to me like a highway/fuel economy motivated gearing. We have another van with a 7.5L and 4.10 gears, and it seems to pull better despite the slightly lower HP and torque. Since we don't do much highway driving, it made sense to look at gearing the rear end with a bigger gear to accommodate the type of work it does.
I believe when ordered new, this van came with 3.73, but could be ordered with 4.10 for towing applications. So a 4.10 should be fine. But, I think that 4.10 was a "compromise" ratio that improved towing without sacrificing fuel economy too much. That's great for applications that spend a lot of time on the highway. But, since we don't need the top end much, and are not too worried about the MPG, and since the 4.10 "compromise" doesn't take into account our 8000' elevation, I started thinking that 4.30 or 4.56 might be a better choice.
Thread Starter
|
Senior User
Joined: Jul 2009
Posts: 295
Likes: 0
From: Rocky Mtns. of Colorado
From the Novak calculator, at 70 MPH, which is about as fast as this van would ever need to go, the current 3.73 gears would have the RPM at 2925 in 3rd and 2080 in OD.
Here are the RPM calculations at 70 MPH for all of the gearing ratios that I'm considering:
Ratio 3rd OD
3.73 2925 2080
4.10 3215 2290
4.30 3370 2390
4.56 3575 2540
I don't know how or if this would affect shift points, and if that is something that I would need to factor in. But, even the 4.56 gearing would only be moving the RPM up about 500, so none of these options seem "extreme" to me.
Mark, you seem to be the resident expert here, what are your thoughts?
Thanks!
Here are the RPM calculations at 70 MPH for all of the gearing ratios that I'm considering:
Ratio 3rd OD
3.73 2925 2080
4.10 3215 2290
4.30 3370 2390
4.56 3575 2540
I don't know how or if this would affect shift points, and if that is something that I would need to factor in. But, even the 4.56 gearing would only be moving the RPM up about 500, so none of these options seem "extreme" to me.
Mark, you seem to be the resident expert here, what are your thoughts?
Thanks!
Frmr Ford Trans Engr
Joined: Aug 1999
Posts: 24,704
Likes: 2,625
From: SE Florida
The computer will automatically adjust the shift points.
I think for your use you will be happiest with the 4.56 ratio.
I think for your use you will be happiest with the 4.56 ratio.
Trending Topics
Thread Starter
|
Senior User
Joined: Jul 2009
Posts: 295
Likes: 0
From: Rocky Mtns. of Colorado
Thanks again Mark. I was afraid that 4.56 might be too much...as they say, too much of a good thing... But, given the application, it makes sense. It just seems like a big jump. So, once this is done, I expect that I'll have to reprogram the computer so that my speedometer is accurate. Can someone tell me how this is done?
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
AEV FXL Super Duty - the Super Duty Raptor Ford Doesn't Make
Brett Foote
Lobo Vs Lobo: Proof the F-150 Lobo Should Be Even Lower!
Michael S. Palmer
Ford's 2001 Explorer Sportsman Concept Looks For a New Home
Verdad Gallardo
10 Best Ford Truck Engines We Miss the Most!
Joe Kucinski
2026 Shelby F-150 Off-Road: Better Than a Raptor R?
Brett Foote
2027 Super Duty Carhartt Package First Look: 12 Things You NEED to Know!
Michael S. Palmer
10 Most Surprising 2026 Ford Truck Features!
Joe Kucinski
Top 10 Ford Trucks Coming to Mecum Indy 2026
Brett Foote
5 Best / 5 Worst Ford Truck Wheels of All Time
Joe Kucinski
Frmr Ford Trans Engr
Joined: Aug 1999
Posts: 24,704
Likes: 2,625
From: SE Florida
It's easy. Change to the 4.56 and drive it. The speedo doesn't care. It reads rear wheel speed, so the gear change doesn't affect it.
2540 RPM at 70 MPH is a bit too high for me for driving across the country, but for what you use it for I think it will work great.
To get a feel for it run the van at 70 MPH with the OD off. That will give you 2900 RPM, which is 400 more than the 4.56 will do in overdrive at 70 MPH.
2540 RPM at 70 MPH is a bit too high for me for driving across the country, but for what you use it for I think it will work great.
To get a feel for it run the van at 70 MPH with the OD off. That will give you 2900 RPM, which is 400 more than the 4.56 will do in overdrive at 70 MPH.
Thread
Thread Starter
Forum
Replies
Last Post
kelrod58801
1968-Present E-Series Van/Cutaway/Chassis
1
Jun 9, 2012 07:07 PM
robertbourque
1968-Present E-Series Van/Cutaway/Chassis
17
Nov 5, 2006 06:05 PM
dlpinkc
Clutch, Transmission, Differential, Axle & Transfer Case
5
Feb 18, 2006 09:35 AM
cranes
1968-Present E-Series Van/Cutaway/Chassis
12
Feb 22, 2005 04:20 PM